Experiencing the vastness of Greenland from a helicopter presents a profound challenge in grasping the true scale of the landscape. There have been moments when I believed we were gliding just above the undulating waves of a fjord, only to catch sight of a diminutive shadow of a seabird below, leading me to realize that what I had initially perceived as floating fragments of ice were, in fact, icebergs the size of office buildings.

At times, I have felt as though we were suspended high above an expanse of uniform, icy terrain, until we gently descended, revealing that the ice lay merely a few meters beneath us.

Crevasses—cracks in the glacier surface—epitomize this perplexing range of scales. Resulting from stresses at the ice’s surface, their orientation and dimensions reveal the dynamics of the ice sheet as it flows toward the ocean.

In the more remote regions, far from the rapid currents that release massive quantities of icebergs into fjords, crevasses can be mere millimeter-wide fissures. However, as the ice accelerates, they can expand to several meters in width, often obscured by misleading snow bridges that necessitate proper safety protocols and rescue training to navigate.

Where the ice meets the ocean, crevasses can grow into colossal spans exceeding 100 meters from wall to wall, and they are increasingly proliferating throughout Greenland.

Scientists have anticipated the expansion of crevasses in Greenland as a consequence of ocean warming, which has consequently accelerated the flow of the ice sheet, enhancing the stress on its surface. Nevertheless, due to the inadequate data from satellites and on-the-ground fieldwork, we previously lacked clarity on the extent and rapidity of these changes.

Mapping Crevasses

In a recent study, my colleagues and I meticulously mapped crevasses across the entire Greenland ice sheet using data from 2016 and 2021. We leveraged the “ArcticDEM,” which consists of three-dimensional surface models derived from high-resolution satellite imagery.

Employing advanced image-processing methodologies on over 8,000 maps, we estimated the volume of water, snow, or air required to “fill” each crevasse, enabling us to calculate their depths and volumes while also observing their evolution over time.

Our findings revealed that between 2016 and 2021, there were significant increases in crevasse volume within the ice sheet’s rapidly flowing sectors. Notably, in the southeastern regions—particularly vulnerable to ocean-induced acceleration and retreat—crevasse volume surged by over 25 percent.

Surprisingly, however, the overall volume of crevasses across the entire ice sheet increased by only 4.3 percent, indicating a more balanced total than anticipated given the considerable growth in certain areas.

This discrepancy can be attributed to a specific outlet glacier, Sermeq Kujalleq (Danish: Jakobshavn Isbræ), the fastest-flowing glacier on Earth. This glacier, moving at nearly 50 meters daily, significantly contributes to Greenland’s overall sea-level rise.

In 2016, Sermeq Kujalleq responded to an influx of cold North Atlantic water by slowing down and thickening. During this period, the crevasses on its surface began to close, thereby counterbalancing increases observed elsewhere in the ice sheet.

This brief deceleration has since ended. Since 2018, Sermeq Kujalleq has accelerated and thinned again due to ongoing environmental warming. Thus, we cannot rely on it to mitigate crevasse growth across the ice sheet in the future.

The Evolution of Crevasses

Crevasses are integral to the life cycles of glaciers, and their expansion poses a serious threat to ice-sheet stability, potentially exacerbating ice loss. They facilitate the downward movement of surface meltwater into the glacier, where it can warm the ice or lubricate the base over which the glacier slides, both of which accelerate its flow into the ocean.

Moreover, at the juncture where ice meets sea, crevasses initiate the fractures from which icebergs may calve, thereby increasing the volume of ice entering the ocean.

In summary, crevasses underpin the dynamic processes at play across Greenland and Antarctica. Nevertheless, these processes remain poorly understood, and their future behavior presents the most significant uncertainty in predicting sea-level rise.

Collectively, the increasing outflow of ice could contribute up to an additional 10 meters of sea-level rise by 2300, threatening the existence of 75 percent of cities housing over five million residents, all situated less than 10 meters above sea level.

It is imperative to deepen our understanding of these mechanisms, including the role of crevasses, to ensure that our projections for sea-level rise are informed and actionable, forming a basis for confronting the global challenges posed by climate change.

Since 2023, an international alliance of polar scientists has been advocating for the global community to limit warming to 1.5?C in a bid to avert the most catastrophic scenarios for global glaciers and ice sheets. Recent reports from the EU’s Copernicus Climate Change Service have confirmed that 2024 marks the first year in which average global temperatures exceeded this critical threshold.

Each incremental increase in temperature warrants significant concern. There remains a glimmer of hope to mitigate the worst consequences of climate change; however, time is fast running out.

Tom Chudley, Leverhulme Early Career Fellow, Department of Geography, Durham University

This article is republished from The Conversation under a Creative Commons license. Read the original article.